The object of this method is that when the molded product is removed, the residue of reacted mixture in the mixing chamber is removed at the same time. This is made possible by the fact that the plane of separation of the molding tool also extends across the mixing chamber. The mixing apparatus may consist of a mixing head fixed to the molding tool or it may be directly integrated with the wall of the mold.
The disadvantage of such apparatus is that if one of the components moves ahead faster than the others, a small portion of it enters the mold cavity without first being mixed and causes faults in or on the finished molded product.
Various methods have been utilized to overcome this difficulty, e.g. absolute synchronization of the injection of the various components. However, the viscosity of the components varies over the course of time and the pressures in the conduits fluctuate slightly. These irregularities are enough to cause the faults mentioned above. Another disadvantage is that the mixing chamber still contains too much air even when its volume is reduced to about 1 cm.sup.3, and when the components flow into the chamber the air is beaten into the mixture and is liable to form bubbles on the surface of the molding. Previous attempts to overcome this difficulty by either providing restrictors in the overflow of the mixing chamber or by providing deflectors and the like in order to obtain a quiet flow of mixture with a flow front free from bubbles have achieved only a moderate degree of success. Remixing devices were therefore, arranged between the mixing chamber and the mold cavity. These devices consisted for example, of a system of channels which branch and recombine. This makes the whole apparatus very complicated and expensive to manufacture. Moreover, the sealing problems are increased and the material wastage when producing the molded products is relatively high.
It is an object of this invention to provide an method by which perfect molded products can be produced, i.e. products which have no faults due to unmixed component residues or bubbles. The molded article should preferably be produced without loss of material in sprue channels.